In a typical method for detecting a target nucleotide sequence, a probe DNA having a nucleotide sequence complementary to that sequence is synthesized, and hybridization of the probe DNA with a target nucleic acid is detected. The hybridization process typically consists of preparing a probe coupled to a fluorescent substance or radioactive isotope, such as a probe labeled with a fluorescent substance or radioactive isotope, hybridizing the probe with DNA that contains a target nucleotide sequence, and detecting a signal emitted by the label by measuring the fluorescent intensity or radioactivity. In addition, in a method for detecting a target protein or a small molecule, a substance capable of binding to the target, such as an antibody, ligand or receptor, is labeled with a fluorescent substance or radioactive isotope, and then measuring the fluorescent intensity, radioactivity or enzyme activity.
Although improvement of those methods has made it possible to detect a target molecule at concentrations on the nanomolar level, there is a growing demand in the art for detection methods with even higher sensitivity. In addition, since a spectrophotometer or fluorescent microscope is required for measuring fluorescence, and a scintillation counter is required for measuring radioactivity, detection of target molecules by conventional methods requires expensive and large equipments. Furthermore, since the majority of conventional methods require separation of label that has been bound to the target and label that has not bound to the target (bound/free (B/F) separation), which makes the procedure complicated. Consequently, there is a need for the development of a simple detection method that does not require special analytical instruments or B/F separation.
Thus, an object of the present invention is to provide a novel method for detecting a target molecule with a simple process and a high sensitivity.